Apparatus for and method of severing film

ABSTRACT

Process of severing film including the steps of subjecting the film to heat and pressure along the desired line of parting to weaken the film and cooling the heated area and effecting severing by pulling the film on either side of the line of parting with a snapping action. Apparatus is provided for performing the above described method of severing.

United States Patent Dyer et a1. [4 May 30, 1972 [54] APPARATUS FOR ANDNIETHOD OF [56] References Cited SEVERING FILM UNITED STATES PATENTS 721t:GealdB.D;Ed t 1 men Kilfgston g; l'l' h of 3,186,628 6 1965 Rohde..229 66 2,191,497 2/1940 Potdevin et al... ....225/96 [73] Assignee: DuPont of Canada, Limited, Montreal, 2,429,944 10/ 1947 Rayburn et al...225/4 P.Q., Canada 3,039,664 6/1962 Harrison et a1. ...225/96 X [22]Filed: g 18 1970 3,160,273 12/1964 Reuther et a1. ..225/96 X [21] Appl.No.: 64,794 Primary Examiner-Frank T. Yost Attorney-Hoge T. SutherlandRelated US. Application Data [63] Continuation of Ser. N0. 826,934, May22, 1969, [57] ABSTRACT abandoned- Process of severing film includingthe steps of subjecting the film to heat and pressure along the desiredline of parting to U.S. .-225/2, weaken the a d cooling the heated areaand effecting 225/100 severing by pulling the film on either side of theline of parting [51] Int. Cl. ..B26f 3/02, B26f 3/06 with a Snappingaction Apparatus is provided f performing [58] Fleld of Search ...225/2,93.5, 96, 100, 96.5, the above described method ofsevering 6 Claims, 4Drawing Figures PATENTEnmwso m2 3,666,151

sum 1 or 2 INVENTORS GERALD B. DYER EDWIN SZPAK BY W o W4 ATTORNEYPATENTEDMAY 30 I972 SHEET 2 0F 2 INVENTORS GERALD B. DYER EDWIN SZPAK BYsk /L 0" 3M ATTORNEY APPARATUS FOR AND METHOD OF SEVERING FILM Thisapplication is a continuation of Ser. No. 826,934 filed May 22, 1969,now abandoned.

This invention relates to the cutting or severing of thermoplastic filmand more particularly to an improved method of severing laminatedthermoplastic film made from two or more monaxially oriented sheets.

In many film processes, thermoplastic film or tubing must be cut tolength before subsequent operations, such as folding. The act of cuttingthe tube, however, frequently causes blocking or scaling to take placealong the cut edge and as a result it is difficult to open the end ofthe tube length. This problem is particularly acute with laminatedoriented tubing made from two or more monaxially oriented films which iscoming into general use for industrial shipping bags.

Perforation methods are not suitable because during snapping the tearfrequently propagates along the lines of orientation rather than acrossthe sheet.

It is, therefore, an object of the present invention to provide animproved method of severing oriented films.

Another object is to provide a method of heat treating a thermoplastictube which permits the tubing to be severed or parted along a patternsuitable for complex bag structures.

Accordingly, there is provided a process for severing orientedthermoplastic film or oriented thermoplastic film laminate whichcomprises subjecting the film to heat and pressure along the desiredline of parting to weaken the film, cooling the heated area andeffecting severing by pulling the film on either side of the line ofparting with a snapping action.

There is also provided a process for producing cut tube lengths from acontinuous sheet of oriented thermoplastic film or orientedthermoplastic film laminate which comprises:

subjecting the film to heat and pressure along the desired line ofparting to weaken the film, said line of parting having sufficientstrength after cooling to permit the continuous sheet to be manipulatedand handled through additional process steps but weak enough to permitthe various sections of the sheet to be separated from each other by asnapping action;

cooling the heated areas;

folding the sheet of film over on itself to form a tube;

applying an adhesive to form a longitudinal seam along the length of thetube;

separating the tube lengths from each other by pulling the film oneither side of the line of parting with a snapping action.

In addition, the present invention provides an apparatus for severingoriented thermoplastic film or oriented thermoplastic film laminatewhich comprises:

a conveyor means for transporting the film;

a heated bar adapted to be brought into pressure contact with said filmalong a predetermined line;

means to cool the area of the film heated by said heater bar and meansto grip the film on either side of said predetermined line of contactwith said heated bar and adapted to produce a snapping action on saidfilm to effect parting.

The present invention also provides an apparatus for producing cut tubelengths from a continuous sheet of oriented thermoplastic film ororiented thermoplastic film laminate which comprises:

a conveyor means for transporting the film;

a heated bar adapted to be brought into pressure contact with said filmalong a predetermined line;

means to cool the area of the film heated by said heated bar,

a tubing section adapted to form said film into a tube;

an adhesive applicator to form a longitudinal seam along the length ofthe tube and means to grip the tube on either side of said predeterminedline of contact with said heated bar and adapted to produce a snappingaction on said tube to effect parting.

These and other objects of the present invention will become evidentfrom the more detailed description set forth below, it being understoodthat such more detailed description is given by way of illustration andexplanation only and not by way of limitation, since various changestherein may be made by those skilled in the art without departing fromthe scope or spirit of the present invention.

The present invention may be more clearly understood by reference to thedrawings in which:

FIG. 1 illustrates a sample apparatus for heat treating film.

FIG. 2 illustrates a modified arrangement for heat treating that may beused to advantage for a patterned cut.

FIG. 3 is a schematic drawing of an apparatus which may be used toproduce a tube cut to length.

FIG. 4 illustrates a sheet of film heat treated to produce a patternedcut.

Referring to FIG. 1, in operation, a length of film l is indexed forwardby nip rolls 2 and 7 and stopped at the predetermined length. Rubbercoated roller 3 which acts as a bed plate for the heat treating step isdriven synchronously with nip rolls 2 and 7 to assist in transportingthe film. The heat treating blade 4 is maintained at a controlledtemperature and is mounted by means not shown so that it may be raisedand lowered. A sheet of polytetrafluoroethylene coated glass fiber cloth5 is usually provided to prevent sticking of the bar to the film. Toeffect the heat treating, the bar is pressed against the film at apredetermined pressure and for a predetermined dwell time. The bar islifted and a cool air blast applied through cooling tube 6. The film isthen conveyed forward. Parting is effected by a snapping action at alater stage which is not shown in FIG. 1.

FIG. 2 is a schematic diagram of an apparatus which may be used toadvantage when a patterned cut is desired. Nip rolls 1 1 and 12 and belt15 are actuated to bring a length of film forward to the pre-cutting orpre-severing section. A polytetrafluoroethylene coated heat treating baror blade 8 is lowered by a cam or some other device to come into contactwith the stationary film for a predetermined dwell time. Bed plate 10prevents distortion of the film and belt. Cooling air is providedthrough distributor 13 to cool the treated area after the blade 8 islifted. The film is indexed forward by nip-rolls l1 and 12 and the heatsevering process repeated on the next section of film.

FIG. 3 is a schematic diagram of an apparatus for producing tubing witha straight or patterned cut.

Film is fed from an unwind stand 16 through a pair of nip rolls 17, aset of dancing rolls 18, onto belt 36 which is carried on rolls 23 and24. Nip rolls l9 and 20 and belt 36 are synchronized to provide anintermittent feed of predetermined length. When the film is stationary,heat treating bar or knife 26, operated by a cam or some other device,descends to contact the film for a predetermined time. Bed plate 22prevents distortion of the film and a polytetrafluoroethylene coating 27prevents the blade from sticking to the film. The blade 26 is raised andcold air is blown through tube 28 to cool the film. Nip rolls 19 and 20and belt 36 are actuated to index a new length of film forward. Dancingrolls" 29 permit the next steps to be operated continuously. Nip 33 isdriven at constant speed and at the same speed as the unwind speed.

The sheet is formed into a tube by tubing section 30 and an adhesive isapplied by applicator 31 to form a longitudinal seam running the lengthof the sheet. This seam is pressed by nip rolls 32.

Hot melt adhesives may be used to advantage with such an arrangement.Suitable hot melt adhesives include polyethylene, copolymers ofethylene, mixtures of polyethylene with elastomers and polyurethane typeadhesives. Solvent based adhesives may also be used provided a suitabledrying section is added.

The tube continues on through constant speed rolls 33 and hence to niprolls 34. These nip rolls 34 are provided with an eccentric drive toproduce the necessary snapping action to effect severing or parting ofthe tube. Tubes cut to length are delivered to stack 35.

EXAMPLE 1 The following tests were conducted on equipment similar tothat shown in FIG. 1. The heat treating bar had a blade with a radius ofl/32inch. The rubber coated roll had a durometer hardness of 40 (ShoreType A-2).

A 2.4 mil thick cross laminate of two monaxially oriented films, eachwith orientation at 45 to the machine direction, was prepared from anethylene-butene copolymer by stretching approximately 4:1. This laminatewas treated with the heat treating blade and then allowed to cool. Goodtreatment was judged to be that which gave weakening of the film butwhich allowed the film to be conveyed forward to subsequent processingsteps. Temperature versus dwell time contiltions which resulted in asatisfactory heat treatment are as follows:

TABLE I Heat Treatment of Laminate Film (Blade Pressure 30 lb.)

After the treatment, parting was readily accomplished by a snappingaction.

EXAMPLE II A laminate as described in Example I was treated on anotherapparatus which gave a patterned treatment as shown in FIG. 4. The heattreating blade edge was l/l6inches wide and nip pressure 40 lb. The fiatbase plate was covered with rubber of 37 durometer hardness (Shore TypeA2). At a dwell time of 0.3 seconds, a temperature of 240 to 250 C. wasfound to give satisfactory treatment. Parting was readily effected by asnapping action.

It is believed that the heat treatment discussed above causesdisorientation to take place along the line where the heat is applied.In addition, there may be also some localized thinning of the film. Aloss of orientation would cause a great localized reduction in tensilestrength and this would act as a tear strip. In any event this treatmentis elfective in causing local weakening so that a snapping action causesseparation.

Thermoplastic film materials which are suitable for use in the presentinvention include:

polyethylene polypropylene polyamide polyester polystyrenepolyvinylchloride and copolymers of ethylene We claim:

1. A process for severing oriented thermoplastic film or orientedthermoplastic film laminates which comprises subjecting the film to heatand pressure along the desired line of parting to weaken the film,cooling the heated area and effecting severing by pulling the film oneither side of the line or parting with a snapping action.

2. The process as claimed in claim 1 in which said thermoplasticmaterial is selected from a list comprising:

polyethylene polypropylene polyamide polyester polystyrenepolyvinylchloride and copolymers of ethylene.

3. The process of claim 1 wherein the dimensions of the film along thedesired line of parting remain substantially the same after beingsubjected to the heat and pressure and being cooled.

4. The process for severing a continuous sheet of oriented thermoplasticfilm or oriented thermoplastic film laminates into separate sectionswhich comprises:

subjecting the film to heat and pressure along the desired line ofparting to weaken the film, said line of parting having sufiicientstrength after cooling to permit the continuous sheet to be manipulatedand handled but weak enough to permit the various sections of the sheetto be separated from each other by a snapping action;

cooling the heated areas;

separating the sections of the sheet from one another by pulling thefilm on either side of the line of parting with a snapping action.

5. The process of claim 4 in which said thermoplastic material isselected from a list comprising:

polyethylene polypropylene polyamide polyolef'm polyester polystyrenepolyvinylchloride and copolymers of ethylene.

6. An apparatus for severing oriented thermoplastic film or orientedthermoplastic film laminate which comprises:

a conveyor means for transporting the film;

a heated bar adapted to be brought into pressure contact with said filmalong a predetermined line;

means to cool the area of the film heated by said heated bar;

and

means to grip the film on either side of said predetermined line ofcontact with said heated bar and adapted to produce a snapping action onsaid film to effect parting.

1. A process for severing oriented thermoplastic film or orientedthermoplastic film laminates which comprises subjecting the film to heatand pressure along the desired line of parting to weaken the film,cooling the heated area and effecting severing by pulling the film oneither side of the line or parting with a snapping action.
 2. Theprocess as claimed iN claim 1 in which said thermoplastic material isselected from a list comprising: polyethylene polypropylene polyamidepolyolefin polyester polystyrene polyvinylchloride and copolymers ofethylene.
 3. The process of claim 1 wherein the dimensions of the filmalong the desired line of parting remain substantially the same afterbeing subjected to the heat and pressure and being cooled.
 4. Theprocess for severing a continuous sheet of oriented thermoplastic filmor oriented thermoplastic film laminates into separate sections whichcomprises: subjecting the film to heat and pressure along the desiredline of parting to weaken the film, said line of parting havingsufficient strength after cooling to permit the continuous sheet to bemanipulated and handled but weak enough to permit the various sectionsof the sheet to be separated from each other by a snapping action;cooling the heated areas; separating the sections of the sheet from oneanother by pulling the film on either side of the line of parting with asnapping action.
 5. The process of claim 4 in which said thermoplasticmaterial is selected from a list comprising: polyethylene polypropylenepolyamide polyolefin polyester polystyrene polyvinylchloride andcopolymers of ethylene.
 6. An apparatus for severing orientedthermoplastic film or oriented thermoplastic film laminate whichcomprises: a conveyor means for transporting the film; a heated baradapted to be brought into pressure contact with said film along apredetermined line; means to cool the area of the film heated by saidheated bar; and means to grip the film on either side of saidpredetermined line of contact with said heated bar and adapted toproduce a snapping action on said film to effect parting.